Sandwich plates find widespread application in aircraft construction by virtue of their extraordinarily favourable ratio between achievable rigidity and weight. For example, floor plates, which are constructed using sandwich plates with a honeycomb-shaped core structure and surface layers of carbon fibre-reinforced epoxy resins fitted on both sides of the core structure, are installed in passenger cabins or in freight compartments. These floor plates, forming the floor above the floor structure of the aircraft fuselage cell, are as a rule individually tailored and separately matched to each type of aircraft. Moreover the floor plates in what are called the wet regions of the aircraft fuselage cell, for example, in the region of toilet facilities, kitchen equipment and in the entrance area into the passenger cabin must be configured so as to be sealed against fluids, as a result of which the installation outlay increases. In normal flight operations of a passenger aircraft the floor plates are themselves subjected to high mechanical loadings in what is often also a chemically aggressive environment. High point loads are caused, for example, by rolling service carts, wheeled suitcases, certain types of shoe heels, and also falling objects.
These result in indentations (so-called “impacts”) of the upper surface layer of the floor plate, and vertical compressions of the core structure in the region of damage. As a consequence of the compressions a further result is spalling of the impregnation of the core structure, as a result of which the latter's strength is severely impaired. Without timely repair of the region of damage in question the latter extends ever further outwards, and can lead to deterioration of the floor plate over a large area. Removal and replacement of the floor plate in question is as a rule not possible in the field, and moreover would also be linked with excessive costs for labour and materials. Moreover as a result of the individual adaptations of the floor plates it would be necessary to maintain a large stock of these plates for each type of aircraft.
In a method of known art for the repair of floor plates in passenger cabins of aircraft all honeycomb cores located in the damage location region are opened up by drilling and filled with a curable synthetic resin material. The connection with the upper surface layer in the region of damage is then filled with a likewise curable plastic material. What is disadvantageous in this procedure is that filling the honeycombs is not possible without the formation of air bubbles, where these preferentially move into the region below the upper surface layer. However, it is exactly in this region, in which from experience the largest distortion of the core structure occurs, that the maximum stabilisation effect is required from the introduced plastic material.
In accordance with a further procedure a drilled hole is firstly introduced into the floor plate in the damage location region. A rotating hook is then inserted through this hole into the sandwich plate, and by means of this hook the core structure is largely destroyed in the region of rotation, so as to create a large cavity to be filled with a curable plastic material for the particular purpose of vertical stabilisation. Subsequently, or earlier in the preparatory work, a further drilled hole is set into the upper surface layer of the floor plate in the region of damage to allow air to escape. Subsequently the indentation that is usually present in the upper surface layer of the floor plate is filled. One advantage of this procedure lies in the fact that in the damage location region only two holes have to be introduced into the floor plate in the region of the surface layer. However, the main disadvantage of this procedure is to be seen in the fact that in the damage location region destruction of the honeycomb-shaped core structure takes place over a large volume.
In a further method variant of previously known art the cells of the core structure in the damage location region are firstly opened up by drilling. A thin fluid, low viscosity, curable plastic material is then introduced into the cells in question. By pivoting and rotating the plate freely in space an even wetting of the cell walls with a stabilising plastic material is effected. However, this method necessarily assumes the removal of the floor plate that is to be repaired.